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Hawaiian Islands Synoptic Discussion and Guidance |
FXHW60 PHFO 280802 RRA
Area Forecast Discussion...Resent
National Weather Service Honolulu HI
1000 PM HST Sat May 27 2017
Light winds will prevail through the holiday weekend, allowing for a
few windward showers during nights and mornings, with clouds and
showers shifting to leeward and interior areas in the afternoons.
Light to moderate trade winds on Tuesday and Wednesday may become
breezy by the end of the week. The returning trade winds will bring
a few brief windward showers, with mostly dry conditions leeward, as
a more seasonable weather pattern develops.
A complex weather pattern prevails across the tropical central north
Pacific this evening, with the islands sandwiched between a pair of
weak surface troughs; one to the NW of Kauai, and one to the SE of
the Big Island. The end result is light winds over the islands and
surrounding waters. The large-scale flow is generally out of the E,
and is currently delivering a few showers to windward portions of
the islands. Meanwhile, clouds and showers that developed in
response to sea breeze convergence over leeward and interior areas
are now slowly dissipating. Water vapor imagery highlights a sharp
trough aloft directly over the island chain, and afternoon soundings
show that this feature has eroded the subsidence inversion and
brought a fair amount of instability. Locally heavy downpours
brought just over 2 inches of rain to SE portions of Kauai in a
relatively short period this afternoon, but elsewhere around the
state, the instability did not result in significant rainfall.
Still a chance the trough aloft promotes the development of a
briefly heavy shower tonight and Sunday, with showers most likely
over windward areas through Sunday morning. The continuation of
light winds on Sunday and Monday will allow the focus for clouds and
showers to shift to leeward and interior areas during the
afternoons. The trough aloft is forecast to move steadily E through
the period, but may still supply sufficient instability to promote
heavy showers over the islands on Sunday, and isolated thunderstorms
to the Big Island slopes, but confidence in this is wavering. Will
wait to see what the 12Z sounding reveals before making changes, if
any, to that portion of the forecast.
By Tuesday the nearby troughs will dissipate and high pressure far
NE of the area will gradually strengthen, and light to moderate
trade winds will gradually strengthen to breezy levels by the end of
the week. A relatively stable atmosphere will allow for a few brief
windward showers, and mostly dry conditions leeward as a
more seasonable weather pattern develops.
The smaller islands will remain under a light wind regime overnight
which mean a land breeze will be taking over in the next couple of
hours. Any showers over land will either dissipate or be nudged into
the adjacent waters. Windward Big Island is still under the
influence of a easterly trade flow, and radar is picking up a few
showers moving into the Puna district. Also, isolated showers along
the Kona coast may linger into early Sunday morning before quiting
for the night.
Otherwise, the prevailing flying condition will be VFR. Brief MVFR
cig and vis are expected with the showers. Tops will be mainly
around 10k but could be as high as 15k feet. AIRMET Sierra for Kauai
will has been dropped, and AIRMET Tango for high level turb over
Kauai to Oahu, has been shifted to between Oahu and Maui. AIRMET
Tango will be extended to 16z and not any further.
A High Surf Advisory remains in effect through Sunday afternoon for
all south facing shores. The current large south swell will
gradually diminish through Tuesday. Please see the latest Coastal
Hazard Message (CFWHFO) on our website for additional information
about the hazardous surf conditions.
The south swell is rolling in on top of higher than normal sea
levels and king tides. Please see the Special Weather Statement
(SPSHFO) product on our website for more information about the
potential impacts from the high tides combined with the large surf.
A northeast swell expected to arrive tomorrow will produce moderate
surf through Monday along east facing shores. North swells will be
very small though Monday. A moderate north northwest swell is
forecast to arrive Monday night, peak Tuesday night, then subside
Winds will remain below the Small Craft Advisory (SCA) threshold
through Memorial Day. Trade winds are forecast to gradually
strengthen starting Sunday night. Winds are expected to reach SCA
speeds around Maui County and the Big Island starting Wednesday.
High Surf Advisory until 6 PM HST Sunday for South facing
shores of all Hawaiian Islands.
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office